Risk Assessment Of Groundwater Pollution In Plain River Network Area

Groundwater is an irreplaceable and important resource for social and economic development in China.However,with the continuous growth of population and the rapid development of industrial and agricultural production,the situation of groundwater pollution is becoming increasingly severe.The risk assessment of groundwater pollution is of great significance to groundwater pollution prevention and groundwater resource management.According to the characteristics of hydrogeological conditions,pollution sources,etc.,this study establishes the risk assessment method of groundwater pollution in plain river network area,and takes Shanghai as an example to evaluate the risk of groundwater pollution,and puts forward the prevention and control measures of groundwater pollution risk.The main conclusions are as follows:(1)The depth to groundwater and permeability coefficient of aquifer in Shanghai are between 0.4-3.1 m and 0.02-3.18 m/d respectively,showing a trend of gradually increasing from west to east and surrounding high and low.The net recharge and aquifer thickness are between 0-412 mm and 0.52-24.60 m,respectively.The net recharge in urban area is far less than that in suburban area.The aquifer thickness is increasing from northwest to southeast.The hydraulic resistance is generally between 0.08-22.8 d,showing a trend of high in the west and low in the east.(2)The groundwater vulnerability in Shanghai is generally high.Above medium level account for 45.27%of area,mainly distributed in southern Chongming,southern Pudong,Jinshan and other regions.The medium level accounts for 33.08%,mainly distributed in northern Chongming,Jiading,central urban area and other regions;the proportion of below the medium level is 21.65%,mainly distributed in Songjiang and Qingpu areas.The results of sensitivity analysis show that the order of effective weights are basically the same as the theoretical weights,and each index removal have a great impact on groundwater vulnerability assessment.(3)The load of pollution sources in the study area is small,ranging from 0 to 4.46.Industrial pollution sources and gas stations have a greater impact,and the impact range is spread throughout the study area;livestock farms,landfills,and hazardous waste disposal sites mainly affect the surrounding areas of Shanghai.The sensitivity analysis results show that the effective weights of the five types of pollution sources are basically consistent with the theoretical weights.(4)The risk of groundwater pollution in Shanghai is relatively small.The "lower" grades are widely distributed in the whole research area,accounting for 43.99%.The area of "medium"level and "low" level is large,accounting for 27.68%and 15.76%respectively;the higher risk areas account for 11.67%,scattered in the whole research area.the high-risk area is relatively small,only accounting for 0.90%of the total area,scattered in Pudong,Jinshan,Qingpu and other regions.The result of groundwater pollution risk assessment is verified by using nitrate as characteristic pollutant,and the correlation coefficient of Spearman is 0.84,which shows that the result of groundwater pollution risk assessment is reasonable.